ATLANTA (CBS ATLANTA) – Cigarettes now contain more nicotine, and are more addictive than researchers had previously believed.

A study from the Department of Public Health and the University of Massachusetts Medical School finds that cigarettes’ “nicotine yield” has sharply increased in the past fifteen years, with the average cigarette delivering nearly 15 percent more nicotine than in 1997.

Although the amount of nicotine has leveled off in that time, the study points to more efficient manufacturing techniques for the rise.

“Cigarettes are getting more efficient at delivering nicotine to smokers,” Thomas Land, a state public health official and principal investigator for the study, told Mass Live. “This could make it more difficult for a current smoker who is trying to quit, and easier for a young smoker to become addicted.”

The change of the cigarette design increased the yield, which is the amount of nicotine present in smoke rather than the cigarette itself. RJ Reynolds, Philip Morris USA, Brown and Williamson and Lorillard tobacco manufacturers were all included in the study.

“It’s important to note that the FDA (U.S. Food and Drug Administration), under its regulatory authority, has received a significant amount of information about cigarette design and manufacturing from Philip Morris USA,” Brian C. May, told Mass Live.

“In addition, the (agency) is currently funding several scientific studies related to nicotine and we will share our perspective, as appropriate, as part of the regulatory process.”

A previous Harvard School of Public Health study had shown that nicotine levels in tobacco products had increased by 10 percent between 1997 and 2005.

According to the Centers for Disease Control and Prevention, an estimated 43.8 million US adults smoke cigarettes – 19 percent of all Americans over 18 years of age.

The CDC reports that smoking is the leading cause of preventable death in the United States, accounting for more than 440,000 deaths annually, or one-in-five of all US deaths. Data from 2010 showed that Utah had the fewest percentage of smokers at 9.1 percent, and West Virginia had the highest rate with 26.8 percent.

Overall, smoking rates are highest in the Midwest and the Southern region of the country.